Conventionally, apparatuses for producing a microemulsion (containing microspheres) and microcapsules have been used in steps of manufacturing chemicals and some processes have been proposed. There are the following processes (see, for example, PCT Japanese Translation Patent Application Publication No. 8-508933): a process in which a second solution is dropped in a first solution, a process in which a first solution is dropped in the air from the inside portion of a double tube and a second solution is dropped from the outside portion thereof, and so on. Among processes for scattering droplets in the air, there is a process for ejecting droplets using piezoelectric elements used for inkjet printers and so on.
On the other hand, a technique in which monodispersed microdroplets are prepared with laboratory equipment is disclosed in Japanese Unexamined Patent Application Publication No. 2000-84384. However, in this technique, there is a problem in that the rate of preparing such microdroplets is low and the microdroplets cannot be covered with surfactants or microcapsule shells. Furthermore, only microdroplets having a diameter three times larger than the width of microchannels can be prepared.